Twitter will soon be able to store location data--that is, latitude and longitude coordinates--on a per-tweet basis, and for your user profile.

Including location information in your tweets will be opt-in only. You will have to visit your Twitter account's settings page on the web site to allow Twitter to store that data. It will not be enabled by default. Even if your Twitter client sends lat/log points along with your status update, if you didn't explicitly opt into including that information, Twitter will drop it at the point of entry and it will not be stored or published.

Users won't see any new features on the Twitter web site when geo launches except for the settings page where you opt in. Twitter is giving API developers a head start to display and transmit geo data in tweets in their apps first.

In practice, expect to see your Twitter client include a checkbox below the posting area labeled something like "include my location with this tweet." If you check the box when you send a tweet but you haven't given Twitter permission to store your location data, you'll have to visit your settings page on the web site to do so.

Interesting: Twitter will scrub geo-data stored in tweets more than 14 days old to avoid subpoenas about a user's location. They will outright delete the location information from their database, not just anonymize it.

While Twitter usually encourages application developers to cache data, in the case of geo, they recommend apps don't keep historical location data so that developers don't become a subpoena target, either. They also recommend "fuzzing" location and time data, so that instead of knowing that Joe Smith was at 8th avenue and 15th street at 2:11PM Eastern time on March 7, 2008, you only show that Joe was in Brooklyn on that day.

The geodata-scrubbing isn't a permanent solution. Twitter is looking into ways to store this data in a "safe" way in the future, so Twitter won't always scrub +14-day-old data, just at first.

Besides just using the free-form text field in the location field already available in your profile, there will be no way to tell Twitter you're in a broad area, say, a city or neighborhood like San Diego. They will only take and store lat/long coordinates. On the front end, they may only display a broad area name, like a city or a neighborhood instead of a specific point, but they will store the specific lat/long coordinates.

Right now, Twitter does support some light geolocation functionality based on the "anything goes" location field in profiles. Try a search for happy hour near:11215 -RT to see tweets (minus retweets) about happy hour in Park Slope, Brooklyn.

This is pretty exciting stuff, if still nascent. Questions? I'll answer what I can in the comments.

Really love that they have done the right thing in scrubbing location data over a period of time. However, I see a couple of potential “issues” with that. How do you deal with the scrubbing of location data after “X” amount of time (in this case 14 days) if you have built some kind of mashup around a certain event (eg: a political rally?) and the people attending – say, everyone at the rally uses a certain hashtag, so you collect all the tweets with that hashtag and associate their location at the time of the tweet for verification. Does the mashup break after 14 days? Certainly, you couldn’t recreate it from re-pulling the data from Twitter, but is the author of the mashup required to delete the location data after 14 days also? And how would that be enforced?
Secondly, Twitter are being socially responsible in deleting the location data after a set period, but what if pressure is brought to bear (by say, a government) for this data to be kept indefinitely. Where does that leave the location-aware tweet? People wishing to subpoena information regarding your location now becomes a 14 day race between you and the lawyers.

This is the thin end of the fantastic wedge that is real-time geolocation publishing for people and things or devices, the latter being underestimated in importance I believe.

Presumably this will rollout globally so how soon after this will Twitter display trending topics by locale to make the service more relevant to glocal users?

On a related note, when do you think we can expect the web interface to be localised into other languages, like Spanish. With competing services apeing Twitter in other languages (FBlite?) Twitter may suffer from uneven market penetration or fail to truly go mainstream everywhere.

How do you deal with the scrubbing of location data after “X” amount of time (in this case 14 days) if you have built some kind of mashup around a certain event (eg: a political rally?) and the people attending – say, everyone at the rally uses a certain hashtag, so you collect all the tweets with that hashtag and associate their location at the time of the tweet for verification. Does the mashup break after 14 days?

In that case, I think the app should collect the data at the time of the event, then after 14 days scrub the individual users’ lat/log coordinates and assign one central coordinate to the entire event, with a radius–’this thing happened in this area.’

Certainly, you couldn’t recreate it from re-pulling the data from Twitter, but is the author of the mashup required to delete the location data after 14 days also? And how would that be enforced?

I think anonymizing it by “fuzzing” the exact location of individual users is what Twitter is encouraging. I’m not sure how and if they will enforce this. I believe geo-centric applications should be upfront about how long they keep data till they fuzz or delete it.

Presumably this will rollout globally so how soon after this will Twitter display trending topics by locale to make the service more relevant to glocal users?

Not sure of the timeline for Twitter proper to roll out geofeatures, but it sure is interesting that they’re letting third party developers at it first, that’s for sure.